Theory Of Operation

Vehicles with saddle fuel tank configurations have two fuel level sending units. The primary side of the tank (left side of vehicle) has the filler tube inlet near the bottom and contains the fuel pump module. During fuel tank fills, fuel must overflow the primary side to reach the secondary side of the tank (right side of vehicle). As fuel is consumed, a siphon tube is used to draw fuel from the secondary side to the primary side. Because the siphon tube flow rate exceeds the fuel consumption rate, the secondary side of the tank will be empty before fuel is depleted from the primary side. The rationality for each fuel level sensor is based on the float position of the opposite side of the tank. The primary sensor (fuel level sensor 1) rationality is enabled when the secondary level is near the bottom of the tank. The secondary sensor (fuel level sensor 2) rationality is enabled before the primary side begins to show fuel consumption or fuel volume is greater than a calibrated volume.